Problem: When I choose the application to open a specific filetype with, it seems to affect other filetypes too. It’s like Dolphin cannot tell the difference between the two different filetypes.

Solution: Probably the KDE platform does not know about one of the two filetypes, so it associates the filetype to a different, known filetype. This is common with XML-based filetypes; even if they use a file extension of their own (e.g. .xliff or .graphml), if they are not a filetype known by the KDE platform, they will be treated as any other XML file, and opened with the default application to open XML files.

Solution: Reindex Baloo. Baloo is a file indexing and search service that Dolphin uses to search for files. It needs to be indexed to work. To solve this problem, in a terminal type, balooctl check

Problem: There is no file transfer dialog.

Solution: As of KDE 5 jobs like file transfers are handled by default in centralized notification system; file transfer is also shown in task manager. To enable separate file transfer dialog disable file transfer tracking on both the System Tray notification area and the task manager plasmoid and re-login.